Just copy and paste the line above that begins and ends with a tilde (~) character into your Exact Form. Then replace the nine with the field identifier of your field. Then replace the word

checkmark

with the Webdings character that is a checkmark by typing a lowercase 'a' on your keyboard. Leave the double quotes that surround the word checkmark alone. Then set the entire line's font, including both tildes, to Webdings. This will make it unreadable, or even more unreadable, but it will work.